external image layercake.GIFPicture (right)
This picture represents the way Federalism has evolved throughout history. In its first stages, Federalism was like a Layer cake, where each of the units of government did not interact very much. Now, Federalism has grown to be much more similar to a marble cake, where all of the different units, although separate, interact with each other.

Website
<www.thefederalismproject.org>
This website is sponsored by the American Enterprise Institute for Public Policy Research. It conducts research on modern-day Federalism in America. It's main topics of research are business regulation (both on a national and state level) and the increasing role of the court system on our society.
It has many specific case studies.